1. Field of the Invention
The present invention relates generally to a semiconductor layer transferring method. More specifically, systems and methods for transferring a thin film from a substrate onto another substrate, a layer of the same area as the substrate, of a thickness from sub-micron to tens of micron, and of the thickness and flatness required by VLSI and MEMS applications, and with sufficiently low defect density in the transferred layer are disclosed.
2. Description of Related Art
Wafer bonding technology can be applied to join two substrates of very different lattice parameters without glue, resulting in a sufficiently high bonding strength such that the bonding interface is as strong as the substrate. The wafer bonding technology has been extended with layer transfer concept in which an etch stop layer is used to fabricate submicron thickness silicon on silicon dioxide to form a silicon on insulator (SOI) material.
The wafer bonding technology combined with layer transfer concept extended the applicable field to include advanced electric materials, opto-electronics materials, and microelectro-mechanical systems (MEMS) fabrication. However, the layer transfer technology based on etch stop concept has some disadvantages, such as the problems related to total thickness variation (TTV) due to uniformity of etch stopping. In addition, the etching process is time consuming and most of substrate is wasted.
A Separation by Implantation Oxygen (SIMOX) method was developed to manufacture SOI substrate. Because the SIMOX-based SOI substrate provides superior uniform thickness, wafer bonding technology may lose its leadership in the field of SOI wafer production if its TTV value is not improved.
U.S. Pat. No. 5,374,564, entitled “Process for the Production of Thin Semiconductor Material Films” to Bruel discloses a layer transfer technology, known as Smart Cut® process. With Bruel's approach, the thickness of bonding-based SOI substrate can be made as well as with the SIMOX-based SOI. In particular, an implantation process is performed first to implant a high dosage of hydrogen ions into a supply substrate and the supply substrate is bonded onto a target substrate. A thermal treating process is then performed to cause the formation of a platelet layer along an implanted peak to separate a layer from the supply substrate and transfer the separate layer onto the target substrate. The Smart Cut® process was quickly adopted into the mainstream SOI substrate manufacturing method as it provides uniform thickness of thin film, less defects in density, no wasted materials, released hydrogen being harmless, and the reusability of the supply substrates.
Another SOI fabrication process, Genesis Process™, developed by Silicon Genesis Corp., uses plasma immersion ion implantation (PIII) technology to implant hydrogen ions into silicon for thin film transferring purposes. This process is similar to the Smart Cut® process but the ion implantation process is replaced with the PIII process and the splitting temperature can be reduced to below 500° C.
Various are other SOI substrate fabrication methods are also known. However, the Smart Cut® and other method transferring processes have several disadvantages. For example, a high dose hydrogen ion implantation process may cause a high defect density in active layer (SOI layer). Defects and deformations in an active layer due to the ion implantation of heavy atoms such as silicon may cause quality issues with the active layer and may be difficult to repair by an annealing process. In addition, the manufacturing is costly due to the use of high ion implantation dosage. Further, a fine void existence of the crystal originated particles or pits (COPs) produced in a bulk wafer, especially in a 300 mm diameter wafer, cannot be totally eliminated and causes severe defect problems in the active layer. The thickness of the transferred layer may be restricted by implantation energy and can be very difficult beyond thickness of microns. The nano size porous silicon formation and following silicon epitaxy growth is complex and relative manufacturing costly. As yet another example, defects of oxide segregation in the active layer due to the oxygen ion implantation process may cause quality issues for IC device manufacturing.
Thus, what is needed is an improved system and method for transfer of an epitaxial layer from a supply substrate onto a target substrate without or with minimal implant damage. Ideally, the process is cost effective and provides a high quality active layer, with reduced COPs defects and reduced implant damage and with excellent and flexile thickness control.